1. Ch. 6 Momentum and Impulse

2. Learning Objectives Explain what characteristics of an object
influence momentum and impulse.
2. Understand how momentum and impulse
affect motion.
Calculate the momentum of a physical
system.
4. Calculate the impulse of a physical system.

3. Momentum

4. Momentum
Momentum is a measure of how hard it is to stop or turn a moving object.
What characteristics of an object would make it hard to stop or turn?

5. Momentum – the product of an object’s mass and velocity
it is a vector quantity
The direction is the same as the velocity
The symbol is “p”

6. Formula
momentum = mass x velocity
p = m x v
(kg•m/s) kg m/s

7. The larger the mass, the greater the momentum compared to a less massive object with the same velocity.
If mass is constant, the larger the velocity the greater the momentum.
A change in momentum over a longer time requires less force

8. Change in momentum
Like any change, change in momentum is calculated by looking at final and initial momentums.
Dp = pf – pi
Dp: change in momentum
pf: final momentum
pi: initial momentum

9. Impulse – the product of the force and
the time over which it acts on
an object which results in a
momentum change of an object or system Δp F= Δt
*unit for Impulse is N*s

10. Impulse

11. Impulsive Forces Usually high magnitude, short duration.
Suppose the ball hits the bat at 90 mph and leaves the bat at 90 mph, what is the magnitude of the momentum change?
What is the change in the magnitude of the momentum?

12. Impulse (J) on a graph area under curve F(N) t (ms) 3000 2000 1000 1 21 2 3 4
t (ms)

13. A change in momentum takes force and time.
The larger the momentum, the more force and/or time it will take to change the momentum

14. Force and time act together to change momentum.

15. FΔt = Δp FΔt = pf - pi FΔt = mvf - mvi
Stopping times and distance depend on the impulse-momentum theorem
Impulse = change in momentum
FΔt = Δp
FΔt = pf - pi
FΔt = mvf - mvi

16. A large force over a short time will have the same effect as a small force over a long time.

17. Pg 209
A 1.7kg volleyball is served at 30m/s. How much momentum does the ball have?

18. Pg. 211
The largest steam powered locomotive was built in the US in It is still operational and is used for entertainment purposes. The locomotive’s mass is 4.85 x 105kg. Suppose this locomotive is traveling northwest along a straight track at a speed of 20.0m/s. What force must the locomotive exert to increase its velocity to 25.0m/s to the northwest in 5.00s?

19. Pg 212
In 1991, a swedish company constructed a forklift truck capable of raising 9.0 x 104kg to a height of about 2m. Suppose a mass this size is lifted with an upward velocity of 12cm/s. The mass is initially at rest and reaches its upward speed because of a net force of 6.0 x 103N exerted upward. For how long is this force applied?